Scheduling Data Transmissions Between a Mobile Terminal and a Base Station in a Wireless Communications Network Using Component Carriers

ABSTRACT

A method of scheduling wireless data transmissions between a mobile terminal ( 701 ) and a base station using multiple component carrier signals is disclosed. The method comprises the steps of: receiving in the mobile terminal information from the base station indicating available component carriers; detecting in the mobile terminal at least one dynamic parameter indicative of the mobile terminal&#39;s current ability to handle component carriers having non-contiguous bandwidths; determining in the mobile terminal in dependence of the at least one dynamic parameter which of the available component carriers to utilize; and transmitting from the mobile terminal to the base station information indicating the component carriers determined to utilize. By doing this the mobile terminal may choose to limit the number of component carriers used in situations where it is disadvantageous, such as situations where the power consumption of supporting multiple component carriers is high or situations where complex hardware is needed.

TECHNICAL FIELD

The invention relates to methods and devices for scheduling datatransmissions between a mobile terminal and a base station in a wirelesscommunications network arranged for the transmission of multiplecomponent carrier signals.

BACKGROUND

With each generation, wireless communication systems are characterizedby ever-higher data rates. While some increase in data rates may beattributed to improvements in modulation, coding, and the like,significant increases in data rates generally require higher systembandwidths. For example, the International Mobile Telecommunications,IMT, advanced (a proposed fourth generation (4G) wireless communicationsystem), mentions bandwidths up to 100 MHz. However, the radio spectrumis a limited resource, and since many operators and systems compete forlimited radio resources, it is unlikely that 100 MHz of contiguousspectrum will be free for such systems.

One approach to increasing bandwidth requirements in limited, fragmentedspectrum is to aggregate non-contiguous spectrum. From a baseband pointof view, this can effectively increase the system bandwidth sufficientlyto support up to 1 Gb/s, a throughput requirement for 4G systems.Transmitting data in non-contiguous parts of the spectrum alsointroduces flexibility, as spectrum utilization may be adapted toexisting spectrum use and geographical position. Additionally, differentmodulation and coding schemes may be advantageously applied to differentportions of the spectrum.

A possible evolution of current cellular systems, such as the 3GPP LongTerm Evolution (LTE), to support non-contiguous spectrum is to introducemultiple component carriers or multiple bands. In such a multi-band ormultiple component carrier system, each separate portion of spectrum maybe considered an LTE system. Multi-band transmission is likely to be aprincipal part of the further releases of 3G LTE targeting ITUIMT-Advanced capabilities. A mobile terminal for use in such a systemwill be capable of receiving multiple component carriers, of differentbandwidths, and transmitted at different carrier frequencies.

US 2007/007090 discloses a multi-carrier communication system in whichradio resources are distributed between a plurality of access terminals.The carriers assigned to an access terminal are determined by thenetwork based on scheduling information received from the accessterminal. The scheduling information may include data requirements,Quality-of-Service requirements, available transmit power headroom, thelocation of the access terminal, or hardware constraints associated withthe access terminal. This disclosure does not relate to the use ofnon-contiguous bandwidths.

The design of a mobile terminal supporting multiple non-contiguouscomponent carriers is non trivial task. The front end radio needs to beable to suppress blocking signal in between the spectrum “chunks”.Different kind of radio architecture can be used for handling thisproblem; however, they typically have drawbacks compared to standardcontiguous system receivers in terms of current consumption. Thereforethere is a need for an efficient non-contiguous multi-carrier LTE systemdesign taking into account the challenges in the mobile terminal frontend receiver design.

SUMMARY

Therefore, it is an object of embodiments of the invention to provide aflexible method of scheduling data transmissions, which is moreefficient and takes the mobile terminal's current ability to handlecomponent carriers having non-contiguous bandwidths into account.

According to embodiments of the invention the object is achieved byusing a method of scheduling data transmissions between a mobileterminal and a base station in a wireless communications networkarranged for the transmission of multiple component carrier signals,each component carrier providing for the transmission of signals in apredetermined bandwidth around the carrier.

The method may comprise the steps of: receiving in the mobile terminalinformation from the base station indicating available componentcarriers, detecting in the mobile terminal at least one dynamicparameter indicative of the mobile terminal's current ability to handlecomponent carriers having non-contiguous bandwidths, determining in themobile terminal in dependence of said at least one dynamic parameterwhich of said available component carriers to utilize for said datatransmissions and transmitting from the mobile terminal to the basestation information indicating the component carriers determined toutilize for the data transmissions.

The mobile terminal may control the number of component carriers used,in relation to a dynamic parameter detected in the mobile terminal. Bydoing this the mobile terminal may choose to limit the number ofcomponent carriers used in situations where it is disadvantageous, suchas situations where the power consumption of supporting multiplecomponent carriers is high or situations where complex hardware isneeded.

In one embodiment the method further comprises the step of selecting theat least one parameter from the group of parameters consisting of aparameter indicative of a charging level of a battery in the mobileterminal, a parameter indicative of a level of transmission power fromthe mobile terminal required to achieve a predetermined quality level ofdata transfer from the mobile terminal and a parameter indicative of alevel of base band processing capability in the mobile terminal.

By letting the mobile terminal control the number of component carrierto use in respect to a parameter indicative of a charging level of abattery in the mobile terminal, a longer battery lifetime may beachieved. This may be done by limiting the use of multiple componentcarriers when the battery charging level is low, thereby saving thepower needed to support multiple component carriers. Additionally asimpler design of the mobile terminal may be used since there is no needfor supporting multiple component carriers at a low battery voltage.

By letting the parameter be indicative of a level of transmission powerfrom the mobile terminal, to achieve a predetermined quality level ofdata transfer, a simpler design of the mobile terminal may be used,since the mobile terminal does not have to support multiple componentcarriers when transmitting with a high power. This may be achieved bylimiting the number of component carriers used when transmitting with ahigh power.

By letting the parameter be indicative of a level of base bandprocessing capability in the mobile terminal a more efficient use of theprocessing resources in the mobile terminal may be achieved. This may bedone by limiting the number of component carriers used when theprocessing resources in the mobile terminal is scarce.

In one embodiment the method further comprises the steps of detectingthe occurrence of a component carrier event triggered by one of theparameter levels passing a predefined threshold; and performing the stepof determining which component carriers to utilize when a componentcarrier event is detected.

By controlling the use of multiple component carriers in respect to anevent triggered by the passing of a predetermined threshold by one ofthe parameter levels, an easy implementation of the method in a mobileterminal is made possible.

In one embodiment the step of transmitting the information indicatingthe determined component carriers uses a Radio Resource Control, RRC,signalling protocol.

In one embodiment the step of transmitting the information indicatingthe determined component carriers uses a Medium Access Control, MAC,signalling protocol.

Some embodiments of the invention relate to a mobile terminal configuredto schedule data transmissions between the mobile terminal and a basestation in a wireless communications network arranged for thetransmission of multiple component carrier signals, each componentcarrier providing for the transmission of signals in a predeterminedbandwidth around the carrier. The mobile terminal is configured toreceive information from said base station indicating availablecomponent carriers; detect at least one dynamic parameter indicative ofthe mobile terminal's current ability to handle component carriershaving non-contiguous bandwidths; determine in dependence of said atleast one dynamic parameter which of said available component carriersto utilize for said data transmissions; and transmit to said basestation information indicating the component carriers determined toutilize for said data transmissions.

Embodiments corresponding to those mentioned above for the method alsoapply for the mobile terminal.

Some embodiments of the invention relate to a computer program and acomputer readable medium with program code means for performing themethod described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described more fully below withreference to the drawings, in which

FIG. 1 is a frequency plot showing multiple component carriers;

FIG. 2 is a flow diagram of a method of scheduling data transmissionsbetween a mobile terminal and a base station;

FIG. 3 a is a frequency plot showing the spectrum leakage whentransmitting multiple component carriers with low power;

FIG. 3 b is a frequency plot showing the spectrum leakage whentransmitting multiple component carriers with high power;

FIG. 4 is a plot showing the battery voltage as a function of the stateof charge;

FIG. 5 a is a frequency plot showing the amplitude of a low energyinterference signal positioned between two component carriers prior tofiltration;

FIG. 5 b is a frequency plot showing the amplitude of a low energyinterference signal positioned between two component carriers afterfiltration;

FIG. 6 a is a frequency plot showing the amplitude of a high energyinterference signal positioned between two component carriers prior tofiltration;

FIG. 6 b is a frequency plot showing the amplitude of a high energyinterference signal positioned between two component carriers afterfiltration; and

FIG. 7 is a functional block diagram of a mobile terminal.

DETAILED DESCRIPTION OF EMBODIMENTS

In a spectrum aggregated or multi-band system as is discussed herein,several frequency bands, contiguous or non-contiguous, may be allocatedfor the communication with one mobile receiver. The modulation andaccess format within the band could be of any kind, e.g., orthogonalfrequency division multiplexing (OFDM), single-carrier frequencydivision multiplexing (SC-FDMA), code-division multiple access (CDMA)etc. In this application, we denote such a system “multiple componentcarrier system”. In this context, one band is referred to as one“component carrier”. It may also be noted that this type of system insome publications is called “multi-carrier”, however this term is alsocommonly used to denote OFDM.

FIG. 1 depicts an example of aggregation of component carriers toachieve greater bandwidth. It may be noted that the left-most componentcarrier is well spaced-apart in frequency to the other componentcarriers. It will experience, and cause, only a small amount of Intercarrier interference due to the wide carrier spacing. However, the tworight most component carriers are not as well spaced apart in frequency.

FIG. 2 shows a flow chart of an embodiment of the present invention. Themobile terminal first, in step 100, detects a multi component carriercell comprising a base station for communicating with the mobileterminal. This may be achieved by using a cell search procedure. Themobile terminal then, in step 110, receives information related to thecomponent carrier possibilities of the multi component carrier cell.This information may include information related to the bandwidth andcarrier frequencies, of the component carriers. The number of possiblecomponent carriers may be any number, including the special case whenonly a single component carrier is available. The mobile terminal then,in step 120, determines a subset of the available component carriers touse for transmitting and receiving data from and to the multi componentcarrier cell, and informs the multi component carrier cell about thissubset. The choice may be based on the physical resources of the mobileterminal. The subset does not have to be a proper subset, meaning thatthe chosen subset may include all the possible component carriersreceived from the multi-carrier cell. Next the mobile terminal connectsto the multi carrier cell, in step 130, and starts to monitor forcomponent carrier events in step 140. Such and event may be related toany dynamic parameter, such as the battery level of the mobile terminal,the transmit power of the mobile terminal, the processing load of themobile terminal, energy of interference signals, or data transferrequirements of application on the mobile terminal. The mobile terminalthen, in step 150, chooses a new subset of the available componentcarriers, after detection of an event and informs the multi componentcarrier cell about the new subset.

In one embodiment the multi component carrier cell is given theopportunity to reject the requested subset of component carriers and mayinstead suggest a different subset.

The communication between the mobile terminal and the multi-carrier cellfor the purpose of configuring the multi-carriers may be achieved byusing a well defined signaling protocol, for instance the Radio ResourceControl (RRC) protocol, the Medium Access Control (MAC) protocol or vialayer 1 signaling.

FIG. 3 a shows frequency leakage when transmitting with low power from amobile terminal to a base station. The transmit power level is typicallychosen based on a predetermined quality level requirement. Closed powerloops are commonly used to adjust the transmit power. The loops functionby monitoring, in the base station, the quality level of thetransmission. If the quality level drops below a predeterminedthreshold, a control signal is sent from the base station to the mobileterminal, which in return increases the transmit power. Reversely, Ifthe quality rises above a predetermined threshold, the base stationsignals to the mobile terminal which then decreases the transmit power.Two disperse component carriers 301, 302 are shown.

Nonlinearities in the transmitter and RF power amplifier result inintermodulation distortion, this leads to frequency leakage. This isespecially a problem when using component carriers with a narrowbandwidth, since they have a high power density in the frequency domain,resulting in significant intermodulation distortion effects. To enableother users to use the bandwidth positioned outside the bandwidth of theused component carriers, strict frequency leakage requirements apply onmobile terminals. 303 shows the frequency leakage of the two componentcarriers 301, 302 and 304 shows the leakage requirement of the mobilenetwork. The frequency leakage 303 of the two component carriers 301,302 is below the leakage requirement 304 when the transmit power of thecarriers is low.

FIG. 3 b shows frequency leakage when transmitting with high power froma mobile terminal to a base station. Two disperse component carriers305,306 are shown. They are positioned at the same frequencies as thetwo component carriers 301,302 in FIG. 3 a, however due to the increasedtransmit power their amplitude is higher. The spectrum leakage of thetwo carriers 307 is now above the spectrum leakage requirement of themobile network. Using a more linear transmitter and RF power amplifier,is a possible way to mitigate this, however highly linear componentsgenerally consumes more power and increases the complexity and cost ofthe mobile terminal.

Using an embodiment of the present invention, the number of componentcarriers may be controlled based on the transmit power of the individualcarriers. One way of doing this is to decrease the number of componentcarriers used, when the transmit power is increased. Alternatively, useof component carriers with a narrow bandwidth may be limited, whentransmitting with high power. This will enable multi-carrier support onmobile terminals without the need of costly hardware and with reasonablepower consumption.

FIG. 4 shows a plot of the voltage, for a typical battery used in mobileterminals, as a function of the state of charge. The state of charge isvaried from 0% to 100%. Three distinct phases are shown, aninitialization phase 401, where the battery voltage drops a smallamount, a plateau phase 402 where the battery voltage is almostunchanged, and a terminal phase 403, where the battery voltage falls tozero. The function of the mobile terminal is unaffected by the voltagechanges in the initialization phase 401 and the plateau phase 402.However in the terminal phase the battery fails to supportfunctionalities of the mobile terminal, and the mobile terminal is inthe end forced to turn off. More linear transmitter blocks and inparticular a more linear power amplifier are needed in a mobile terminalsupporting multiple component carries, these however have a high powerconsumption. A mobile terminal supporting multiple component carrierswill therefore cease to function relative early in the terminal phase.

However by using an embodiment of the present invention the number ofcomponent carriers may be controlled based on the state of charge of thebattery in the mobile terminal. This may be done by decreasing thenumber of component carriers used, when the state of charge of thebattery is low, thereby achieving both multi carrier support and a longbattery life time, without the need of a complex and expensivearchitecture in the mobile terminal.

According to an embodiment of the invention the number of componentcarriers used may be controlled by a power management system functioningas a dynamic parameter. The power management system may function byestimating the power consumption of supporting multiple componentcarriers and determine the number of carriers to use in relation to theestimated power consumption. This may be done by limiting the number ofcomponent carriers used when the power consumption for supportingmultiple component carriers is high. The state of charge of the batteryin the mobile terminal may also be used as an input to the powermanagement system. By using a power management system a longer batterylife time is achieved.

Thereby multiple component carriers may be only be supported insituations where the power consumption for supporting them are relativelow.

FIG. 5 a shows a frequency plot of a low energy interference signal 502positioned between two component carriers 501,502 prior to filtration ina mobile terminal. 504 is a threshold showing the ability of the filtersin the mobile terminal to block out interference signals. The thresholdis determined by the quality of the filters in the mobile terminal. Theinterference signal 502 has an amplitude that is lower than thethreshold 504. FIG. 5 b shows a frequency plot of the same situation asdepicted in FIG. 5 a, after filtration in the mobile terminal. The powerof the interference signal has been minimized to an insignificant level,and a good quality of service is achieved for the two component carriers501,502.

FIG. 6 a shows a frequency plot of a high energy interference signal 602positioned between two component carriers 601,602 prior to filtration ina mobile terminal. 604 is a threshold showing the ability of the filtersin the mobile terminal to block out interference signals. The amplitudeof the interference is in this situation higher than the threshold 604.FIG. 6 b shows a frequency plot of the same situation as depicted inFIG. 6 a after filtration in the mobile terminal. The power of theinterference signal has been lowered, but it remains relative highcompared to the amplitude of the two component carriers 601,602resulting in a poor quality of service of the carriers. This can becorrected by using high performance filters with a higher threshold;however this will again will both increase the total power consumptionand increase the overall cost of the device.

Using an embodiment of the present invention, the number of usedcomponent carriers may be controlled based on the power of interferencesignals. This may be achieved by limiting the use of multi carriercomponents when high energy interference signals are present, therebyachieving good multi carrier support in the most common case, when nohigh energy interference signals are present, without the need of costlyhardware to cope high energy interference signals.

Mobile terminals have transformed from being a simple communicationtools into being a fully operational transportable computer system,providing a range of different applications such as audio and movieapplications, maps, dictionaries and games. This evolution has increasedthe need for processing power in mobile terminals. Multi carriercomponent support further increases the overall processing load of themobile terminal. Complicated application will therefore be processedslower when multi carrier components is used, resulting in a decreaseduser experience. By using an embodiment of the present invention, thenumber of component carriers used, may be controlled in relation to theprocessing load of the mobile terminal. This can be achieved by usingfewer component carriers when processing complicated application,thereby securing a faster processing of complex application and anincreased user experience.

FIG. 7 shows a functional block diagram of a mobile terminal 701configured to schedule data transmissions between the mobile terminaland a base station in a wireless communications network using theprinciples of the present invention. The mobile terminal comprises anantenna 702 for communicating with the base station using RF signals.The RF signals from the antenna is received in the RF block 703 andtransmitted to the DET block 704, where the mobile terminal 701 receivesinformation from the base station indicating available componentcarriers. The mobile terminal then in block 706 detects at least onedynamic parameter indicative of the mobile terminal's current ability tohandle component carriers, where the component carriers may form acontiguous or non-contiguous bandwidth. The at least one dynamicparameter detected in 706 together with the available component carriersdetected in 704 are send to a control block 705 where the mobileterminal 701 determines a subset of the available component carriers touse for transmitting and receiving data from and to the base station,and informs the base station about this subset. The subset does not haveto be a proper subset, meaning that the chosen subset may include allthe possible component carriers received from the multi-carrier cell.

According to an embodiment of the present invention the number ofcomponent carriers used may be determined in relation to a combinationof different dynamic parameters. The combination may be any combinationof the following parameters; the battery level of the mobile terminal,the transmit power of the mobile terminal, the processing load of themobile terminal, energy of interference signals, or data transferrequirements of application on the mobile terminal. E.g. a mobileterminal functioning accordingly to the present invention may controlthe number of component carries used in respect to both the batterylevel is and the transmit power.

Although various embodiments of the present invention have beendescribed and shown, the invention is not restricted thereto, but mayalso be embodied in other ways within the scope of the subject-matterdefined in the following claims.

1-13. (canceled)
 14. A method of scheduling data transmissions between amobile terminal and a base station in a wireless communications network,the base station configured to transmit multiple component carriersignals, each component carrier configured to carry transmitted signalsin a predetermined bandwidth around the carrier, the method comprising:receiving, at the mobile terminal, information from said base stationindicating available component carriers; detecting, at the mobileterminal, at least one dynamic parameter indicating the mobileterminal's current ability to handle component carriers havingnon-contiguous bandwidths; determining, at the mobile terminal, which ofsaid available component carriers to utilize for said data transmissionsbased on said at least one dynamic parameter; and transmitting, fromsaid mobile terminal to said base station, information indicating thedetermined component carriers to utilize for said data transmissions.15. The method of claim 14 further comprising selecting said at leastone dynamic parameter from a group of parameters consisting of: aparameter indicating a charging level of a battery in the mobileterminal; a parameter indicating a level of transmission power from themobile terminal required to achieve a predetermined quality level ofdata transfer from the mobile terminal; and a parameter indicating alevel of base band processing capability in the mobile terminal.
 16. Themethod of claim 15 further comprising: detecting an occurrence of acomponent carrier event triggered by one of said parameters in the groupof parameters passing a predefined threshold; and determining whichcomponent carriers to utilize when the component carrier event isdetected.
 17. The method of claim 14 wherein transmitting theinformation indicating the determined component carriers comprisestransmitting the information using a Radio Resource Control (RRC)signalling protocol.
 18. of the method of claim 14 wherein transmittingthe information indicating the determined component carriers comprisestransmitting the information using a Medium Access Control (MAC)signalling protocol.
 19. A mobile terminal configured to schedule datatransmissions between the mobile terminal and a base station in awireless communications network, the base station configured to transmitmultiple component carrier signals, each component carrier configured tocarry transmitted signals in a predetermined bandwidth around thecarrier, the mobile terminal configured to: receive information fromsaid base station indicating available component carriers; detect atleast one dynamic parameter indicating the mobile terminal's currentability to handle component carriers having non-contiguous bandwidths;determine which of said available component carriers to utilize for saiddata transmissions based on said at least one dynamic parameter; andtransmit information indicating the determined component carriers toutilize for said data transmissions to said base station.
 20. The mobileterminal of claim 19 further configured to select said at least onedynamic parameter from a group of parameters consisting of: a parameterindicating a charging level of a battery in the mobile terminal; aparameter indicating a level of transmission power from the mobileterminal required to achieve a predetermined quality level of datatransfer from the mobile terminal; and a parameter indicating a level ofbase band processing capability in the mobile terminal.
 21. The mobileterminal of claim 20 further configured to: detect an occurrence of acomponent carrier event triggered by one of said parameters in the groupof parameters passing a predefined threshold; and determine whichcomponent carriers to utilize when the component carrier event isdetected.
 22. The mobile terminal of claim 19 further configured totransmit the information indicating the determined component carriersusing a Radio Resource Control (RRC) signalling protocol.
 23. The mobileterminal of claim 19 further configured to transmit the informationindicating the determined component carriers using a Medium AccessControl (MAC) signalling protocol.
 24. The mobile terminal of claim 19further configured to communicate data in a Third Generation Long TermEvolution system.
 25. A mobile terminal having a computer programcomprising program code that, when executed at the mobile terminal,configures the mobile terminal to: receive information from a basestation indicating available component carriers; detect at least onedynamic parameter indicating the mobile terminal's current ability tohandle component carriers having non-contiguous bandwidths; determinewhich of said available component carriers to utilize for said datatransmissions based on said at least one dynamic parameter; andtransmit, to said base station, information indicating the determinedcomponent carriers to utilize for said data transmissions.
 26. A mobileterminal comprising: a non-transitory computer readable medium havingprogram code stored thereon, the program code configured to cause themobile terminal to: receive information from a base station indicatingavailable component carriers; detect at least one dynamic parameterindicating the mobile terminal's current ability to handle componentcarriers having non-contiguous bandwidths; determine which of saidavailable component carriers to utilize for said data transmissionsbased on said at least one dynamic parameter; and transmit, to said basestation, information indicating the determined component carriers toutilize for said data transmissions.